【leetcode刷题笔记】

206.反转链表

难度：简单
我写的：（妖魔化双指针，做的时候画图就好）

class Solution {
public:
    ListNode* temp;
    ListNode* reverseList(ListNode* head) {
        if(!head || !head->next) return head;
        ListNode* now = head -> next;
        ListNode* last = head;
        while(head -> next){
            head -> next = now -> next;
            now -> next = last;
            last = now;
            now = head -> next;
            
        }
        return last;        
    }
};

递归写法：
https://leetcode-cn.com/problems/reverse-linked-list/solution/dong-hua-yan-shi-206-fan-zhuan-lian-biao-by-user74/

class Solution {
public:
    ListNode* reverseList(ListNode* head) {       
        if(!head || !head->next) return head;
        ListNode* temp = reverseList(head->next);//函数栈里的临时变量
        head -> next -> next = head;
        head -> next = NULL;
        return temp;//每次函数栈中的temp不变 都是最后一个元素，忘记就回顾链接里的ppt
    }
};

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